A fluorine-based lubricant is widely used for the lubrication of various kinds of machineries such as automobiles, electric equipments, construction machines, information equipments, industrial machines, working machines, and the parts constituting these machineries. In recent years, in association with speeding-up, miniaturization, high qualification and weight saving, the temperature of these peripheral equipments is tended to increase more and more. In addition, there are requirements for anti-rust property at the time when equipments are used in coastal region or at the shipping for export, thus anti-rust characteristics, thermal resistance characteristics and the like are required.
Generally, for the improvement of the anti-rust property, it is proposed to add an additive having thermal resistance to the base oil to improve the performance of the lubricants. For example, in Patent Document 1, a lubricant oil composition comprising a fluorine-containing phosphorous compound is proposed. These lubricant oil compositions improve the abrasion resistance property, anti-rust property and the like without damaging the thermal resistance property. However, these compositions cannot comply with today's increasing requirement for thermal resistance property.
A lubricant oil (a grease) comprising a phosphate ester based compound having the perfluoropolyether group is proposed in Patent Document 2 and a lubricant oil (a grease) comprising an aryl phosphate compound and an aryl phosphonate compound with or without the mono- or poly-alkyleneoxide bonding group between phosphorus and fluorocarbon group is proposed in Patent Document 3. In these additives, since the fluorine-containing group and the phosphate group form C—O—P bond, hydrolysis is liable to occur and as a result thermal resistance and durability becomes poor. As the result, thermal resistance which is the original characteristics of fluorine oil/grease cannot be exerted.
In Patent Document 4, a lubricant used for the magnetic disc containing a stabilizing compound composed by the repeating units of —(CF2)nO— and the terminal group —CH2NRR′ is described. By using the obtained compound as the additive for perfluoropolyether, a good result can be obtained. However, improvement of the stability is further required.
In Patent Document 5, a lubricant whose stability is to be improved utilizing a compound having a pyridine ring is described. The compound having the pyridine ring contributes to the stability of the perfluoropolyether base oil and the obtained lubricant shows an excellent performance. However, for satisfying the increased recent level of the requirement for the anti-rust property, anti-gas property and anti-degradation property, further improvement is required.
In addition, as a lubricant for reducing the abrasion of a sliding member such as an electric contact having a noble metal surface including a gold plating surface or silver plating surface, a copper surface and a copper-alloy surface, a grease composition comprising at least one kind selected from the group consisting of organic zinc compounds and thiazole-based compounds and at least one kind selected from the group consisting of the titanate-based coupling agents and aluminum-based coupling agents is proposed. In addition, a grease composition comprising the quaternary ammonium salt of hectorite as the additive is also proposed (See Patent Documents 6 to 7).
However, the base oil used in these proposals is a synthetic hydrocarbon oil and the application for the fluorine-containing oil is not considered, thus they cannot comply with today's increasing requirement for lubricant in thermal resistance, etc.
As a lubricant containing fluorine-based lubricant which is known to be effective in the improvement of the ant-abrasive property and the like, there can be mentioned a lubricant comprising a phosphonic acid compound in which the perfluoropolyether group is the fluorine-containing group and a lubricant comprising a phosphate ester having the perfluoropolyether group. However, the efficacy of the anti-abrasive property of these lubricant is only confirmed for the steel material which is the mating material, and they are not effective against a noble metal surface, a copper surface and a copper-alloy surface (See Patent Documents 2 and 8)